Proton conducting polymer film and method for production thereof

ABSTRACT

An object of the present invention is to provide a proton conducting polymer membrane that has excellent mechanical properties and high methanol barrier properties, in addition to high proton conductivity, and is useful as an electrolyte in polymer electrolyte fuel cells and direct methanol fuel cells. The present invention provides a proton conducting polymer membrane having a product of a proton conductivity at 23° C. and a methanol barrier coefficient at 25° C. in an aqueous methanol solution of a specified concentration being a specified value or more. The present invention also provides a proton conducting polymer membrane having an ion exchange capacity of 0.3 milli-equivalent/g or more, and having a crystalline phase.

TECHNICAL FIELD

The present invention relates to a proton conducting polymer membraneand a method for manufacturing the same.

BACKGROUND ART

A proton conducting polymer membrane is a major component ofelectrochemical elements for polymer electrolyte fuel cells, humiditysensors, gas sensors, electrochromic display devices and the like. Amongthese electrochemical elements, polymer electrolyte fuel cells areexpected as one of the pillars of a future, new energy technology. Apolymer electrolyte fuel cell (PEFC or PEMFC) using a proton conductingpolymer membrane composed of a polymeric compound as an electrolytemembrane is studied for applications in mobile bodies such asautomobiles, home cogeneration systems, compact portable equipment forconsumers and the like, because of features such as operation in lowtemperatures and possibility of size and weight reduction. Inparticular, a fuel-cell vehicle mounting a PEFC has features such ashigh energy-efficiency and small carbon dioxide emissions, and has beenattracting a growing social interest as the ultimate ecology-car.Moreover, a direct methanol fuel cell (DMFC) using methanol as fuel hasfeatures such as simple structure, easiness of fuel supply andmaintenance and high energy density, and is expected for applications incompact portable equipment for consumers such as cellular phones andnotebook computers as a substitute for lithium ion secondary batteries.

A styrene-based cation-exchange membrane was developed as a protonconducting polymer membrane in 1950s. However, this styrene-basedcation-exchange membrane is poor in stability under the environment foroperating fuel cells, and it was impossible to manufacture a fuel cellwith a sufficient life using this membrane. Perfluorocarbon sulfonicacid membranes typified by Nafion (registered trade mark of EI du Pontde Nemours and Company, the same hereinafter) have been developed as aproton conducting membrane having practical stability and proposed forapplications in many electrochemical elements such as PEFCs.Perfluorocarbon sulfonic acid membranes have high proton conductivityand are excellent in chemical stability such as acid resistance andoxidation resistance. However, they have disadvantages in that it isdifficult to manufacture them and they are very expensive. Furthermore,perfluorocarbon sulfonic acid membranes exhibit high permeation (orcrossover) of hydrogen-containing liquid such as methanol that isconsidered promising as fuel for fuel cells to be mounted on portableequipment for consumers, which is so called a chemical short-circuitreaction. This causes reduction of not only a cathode potential but alsofuel efficiency, and so this is a major factor in the reduction of cellproperties. Therefore, there are many problems in using suchperfluorocarbon sulfonic acid membranes as an electrolyte membrane indirect methanol fuel cells. Moreover, fluorine-containing compoundsimpose a heavy load on the environment when they are synthesized and arediscarded, and so they are not necessarily desirable for components infuel cells or the like that are designed in consideration of the problemof the environment.

Under such a background, there have been proposed various protonconducting polymer membranes of a non-perfluorocarbon sulfonic acid-typecomposed of sulfonated aromatic polymers or the like, as protonconducting polymer membranes that can be easily manufactured and areinexpensive. As representative examples, there are proposed sulfonatesof heat-resistant aromatic polymers such as sulfonated polyetheretherketones (refer to, for example, Japanese Patent Laid-Open No.06-93114), sulfonated polyether sulfones (refer to, for example,Japanese Patent Laid-Open No. 10-45913), sulfonated polysulfones(referto, for example, Japanese Patent Laid-Open No. 09-245818) andsulfonated polyimides (refer to, for example, National Publication ofInternational Patent Application No. 00-510511). Further, there isproposed a proton conducting polymer membrane composed of a sulfonatedSEBS (styrene-(ethylene-butylene)-styrene) which is less expensive andmechanically and chemically stable (refer to Japanese Patent Laid-OpenNo. 10-503788). These sulfonated hydrocarbon polymer membranes can beeasily manufactured at a low cost. However, the proton conductivity ofthese membranes is insufficient for use as the electrolyte membrane inPEFC that requires high proton conductivity. If an increased amount ofproton conducting substituents such as a sulfonic acid group isintroduced in order to improve the proton conductivity, handlingproperties will be considerably impaired, because mechanical propertiesof these membranes are reduced (reduction of strength and/orelongation); the membranes become water-soluble; or water absorption ofthe membranes is increased, thereby considerably swelling the membranes.Moreover, there is a similar tendency also to methanol that is promisingas fuel for fuel cells for compact portable equipment, which may limitthe use of these membranes in this application.

There is also proposed a proton conducting material based onpolyphenylene sulfide, as a sulfonated hydrocarbon polymer with chemicaland thermal stability. However, since polyphenylene sulfide issubstantially insoluble in solvents, it is poor in processability suchas membrane-forming properties compared with other proton conductingmaterials that are soluble in solvents. For example, U.S. Pat. No.4,110,265 discloses a method in which polyphenylene sulfide is reactedwith oleum to prepare sulfonated polyphenylene sulfide for use asscation exchange material. However, since this material is a crosslinkedpolymer that is insoluble in a solvent, it is difficult to use it byfurther processing. Moreover, National Publication of InternationalPatent Application No. 11-510198 proposes a sulfonated polyphenylenesulfide that is soluble in an aprotic polar solvent. This patentdiscloses a method for preparing a polymer that can be easily processedinto a film by imparting solubility in an aprotic polar solvent bymodifying polyphenylene sulfide. However, the method disclosed in thispatent includes various steps such as modification (sulfonation) ofpolyphenylene sulfide, recovery of a modified product by precipitationand drying, preparation of an aprotic polar solvent solution, formationof a membrane and removal of the solvent.

Furthermore, WO02/062896 discloses a method for manufacturing asulfonated aromatic polymer membrane such as a sulfonated polyphenylenesulfide. It describes the use of chlorosulfonic acid as a sulfonatingagent and dichloromethane as a solvent in the method for manufacturing asulfonated aromatic polymer membrane. However, it can be easily assumedthat a sulfonated polymer membrane obtained by this manufacturing methodwill also have increased methanol permeation when an increased amount ofproton conducting substituents such as a sulfonic acid group isintroduced in order to obtain high proton conductivity. Thus, althoughthe electrolyte membrane in direct methanol fuel cells is required tosuppress methanol permeation without reducing proton conductivity, theproton conductivity and methanol barrier properties are in tradeoffrelationship, and so it is difficult that these properties are madecompatible with each other.

Moreover, since halogenated hydrocarbons having low carbon atoms such asdichloromethane have a low boiling point, it can be easily assumed thatauxiliary facilities are required for preventing evaporation of asolvent, recovering an evaporated solvent and the like until asulfonated polymer membrane is obtained, resulting in an increasedmanufacturing cost.

DISCLOSURE OF THE INVENTION

The present invention has been created in view of the above describedproblems, and it is an object of the present invention to provide aproton conducting polymer membrane having both proton conductivity andmethanol barrier properties, which is useful as an electrolyte membranein a polymer electrolyte fuel cell and a direct methanol fuel cell, andto provide a method for manufacturing the same.

Thus, a proton conducting polymer membrane of the present inventionrelates to a proton conducting polymer membrane having a product((S·day)/μmol) of proton conductivity (S/cm) at 23° C. and a methanolbarrier coefficient ((cm·day)/μmol) at 25° C. to an aqueous methanolsolution of a specified concentration that satisfies at least one ofeither (A) or (B) below, wherein

-   -   (A) the product in an aqueous methanol solution of 10% by weight        is 2.5×10⁻⁴ (S·day)/μmol or more, or    -   (B) the product in an aqueous methanol solution of 64% by weight        is 4.5×10⁻⁵ (S·day)/μmol or more.

Furthermore, the present invention relates to a proton conductingpolymer membrane having an ion exchange capacity of 0.3milli-equivalent/g or more, and having a crystalline phase.

The above described proton conducting polymer membrane comprises asulfonic acid group.

The above described proton conducting polymer membrane preferablycomprises a hydrocarbon polymer, and further preferably comprises acrystalline aromatic polymer. More preferably, the crystalline aromaticpolymer is polyphenylene sulfide.

The above described proton conducting polymer membrane preferably has anelongation at break as determined according to JIS K 7127 of 10% ormore.

Moreover, the proton conducting polymer membrane has a protonconductivity at 23° C. of 1.0×10⁻³ S/cm or more, and preferably 1.0×10⁻²S/cm or more.

The above described proton conducting polymer membrane preferably has amethanol barrier coefficient at 25° C. to an aqueous methanol solutionof 64% by weight of 3.0×10⁻⁴ (cm·day)/μmol or more.

Furthermore, the proton conducting polymer membrane is preferablyirradiated with at least one radiation selected from the groupconsisting of γ-ray, electron beam and ion beam. Preferably, the dose ofthe above described radiation is from 10 kGy to 1,000 kGy.

The present invention also relates to a membrane-electrode assemblyusing the above described proton conducting polymer membrane.

At least one catalyst layer of the membrane-electrode assembly comprisesa platinum and ruthenium catalyst.

The present invention also relates to a polymer electrolyte fuel cellusing the above described proton conducting polymer membrane or theabove described membrane-electrode assembly.

The present invention also relates to a direct methanol fuel cell usingthe above described proton conducting polymer membrane or the abovedescribed membrane-electrode assembly.

Moreover, the present invention relates to a method for manufacturing aproton conducting polymer membrane comprising bringing a film comprisinga hydrocarbon polymer into contact with a sulfonating agent to obtain aproton conducting polymer membrane having a product ((S·day)/μmol) ofproton conductivity (S/cm) at 23° C. and a methanol barrier coefficient((cm·day)/μmol) at 25° C. to an aqueous methanol solution of a specifiedconcentration that satisfies at least one of either (A) or (B) below,wherein

-   -   (A) the product in an aqueous methanol solution of 10% by weight        is 2.5×10⁻⁴ (S·day)/μmol or more, or    -   (B) the product in an aqueous methanol solution of 64% by weight        is 4.5×10⁻⁵ (S·day)/μmol or more.

Moreover, the present invention relates to a method for manufacturing aproton conducting polymer membrane comprising bringing a film comprisinga crystalline hydrocarbon polymer into contact with a sulfonating agentto obtain a proton conducting polymer membrane that has an ion exchangecapacity of 0.3 milli-equivalent/g or more and has a crystalline phase.

The above described hydrocarbon polymer is a crystalline hydrocarbonpolymer, and is preferably polyphenylene sulfide.

The above described sulfonating agent is at least one selected from thegroup consisting of chlorosulfonic acid, oleum, sulfur trioxide andconcentrated sulfuric acid.

The above described film is preferably brought into contact with thesulfonating agent in the presence of a solvent, and more preferably, thesolvent is a halide with three or more carbon atoms.

Further, the above described solvent is preferably at least one selectedfrom the group consisting of 1-chloropropane, 1-bromopropane,1-chlorobutane, 2-chlorobutane, 1-chloro-2-methylpropane, 1-bromobutane,2-bromobutane, 1-bromo-2-methylpropane, 1-chloropentane, 1-bromopentane,1-chlorohexane, 1-bromohexane, chlorocyclohexane and bromocyclohexane,and is more preferably 1-chlorobutane.

The above described sulfonating agent is sulfur trioxide, and a filmcomprising a hydrocarbon polymer is brought into contact with a gascontaining sulfur trioxide.

Furthermore, the proton conducting polymer membrane is preferablyirradiated with at least one radiation selected from the groupconsisting of γ-ray, electron beam and ion beam, and more preferably,the dose of the above described radiation is from 10 kGy to 1,000 kGy.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of an essential part of a membrane-electrodeassembly of the present invention;

FIG. 2 is a sectional view of an essential part of a polymer electrolytefuel cell (direct methanol fuel cell) of the present invention;

FIG. 3 is a sectional view of an essential part of a direct methanolfuel cell of the present invention;

Incidentally, in FIGS. 1 to 3, 1 denotes a proton conducting polymermembrane; 2 and 3 denote binder layers; 4 and 5 denote catalyst layers;6 and 7 denote diffusion layers; 8 and 9 denote catalyst loaded gasdiffusion electrodes; 10 denotes a membrane-electrode assembly; 11 and12 denote separators; 13 denotes a fuel channel; 14 denotes an oxidizerchannel; 15 denotes a fuel tank; and 16 denotes a support.

FIG. 4 is an X-ray diffraction chart of a proton conducting polymermembrane in Example 1;

FIG. 5 is an X-ray diffraction chart of a proton conducting polymermembrane in Example 2;

FIG. 6 is an X-ray diffraction chart of a proton conducting polymermembrane in Example 3;

FIG. 7 is an X-ray diffraction chart of a proton conducting polymermembrane in Example 17;

FIG. 8 is an X-ray diffraction chart of a proton conducting polymermembrane in Comparative Example 3; and

FIG. 9 is an X-ray diffraction chart of a proton conducting polymermembrane in Comparative Example 4.

BEST MODE FOR CARRYING OUT THE INVENTION

A proton conducting polymer membrane of the present invention preferablyhas a product ((S·day)/μmol) of proton conductivity (S/cm) at 23° C. anda methanol barrier coefficient ((cm·day)/μmol) at 25° C. to an aqueousmethanol solution of a specified concentration that satisfies at leastone of either (A) or (B) below, wherein

-   -   (A) the product in an aqueous methanol solution of 10% by weight        is 2.5×10⁻⁴ (S·day)/μmol or more, or    -   (B) the product in an aqueous methanol solution of 64% by weight        is 4.5×10⁻⁵ (S·day)/μmol or more.

The proton conductivity in the present invention indicates the mobilityof proton (H⁺) in a proton conducting polymer membrane. It can generallybe calculated by measuring the resistance of a proton conducting polymermembrane using a known alternating current impedance method. Themethanol barrier coefficient indicates the difficulty of methanolpermeation through a proton conducting polymer membrane. The methanolbarrier coefficient is defined by the reciprocal of the methanolpermeation coefficient of a proton conducting polymer membranedetermined by a known method. As an example, a commercially availablemembrane permeation experimental apparatus is used as described below.Ion-exchanged water and an aqueous methanol solution of a specifiedconcentration are separated with a proton conducting polymer membrane.After a lapse of predetermined time, the amount of methanol permeated tothe side of ion-exchanged water is quantified by a gas chromatograph,from which the methanol permeation coefficient is determined. Themethanol barrier coefficient can be calculated by calculating thereciprocal of the methanol permeation coefficient. A flow chart forcalculating the methanol barrier coefficient is shown below.

Note that since the methanol barrier coefficient varies with theconcentration of an aqueous methanol solution to be used, it isnecessary that the methanol barrier coefficient have a desired value inthe concentration of an aqueous methanol solution that is actually used.

In order to achieve excellent power generation properties using a protonconducting polymer membrane of the present invention as an electrolytemembrane in direct methanol fuel cells in which an aqueous methanolsolution is used as a fuel, there are required not only high protonconductivity, but also prevention of the reduction of cell propertiesdue to the permeation of methanol that is a fuel, in other words, highmethanol barrier properties. Since a proton conducting polymer membraneof the present invention has a product of the proton conductivity andthe methanol barrier coefficient of a specific value or more, it ispossible for the membrane to exhibit excellent performance as theelectrolyte membrane in direct methanol fuel cells without deterioratingthe performance due to excessively low proton conductivity or anexcessive amount of methanol permeated.

For example, when a proton conducting polymer membrane of the presentinvention is compared with a membrane that has the same protonconductivity and lower methanol barrier properties and in which theabove described (A) and (B) are not satisfied, the membrane of thepresent invention exhibits a smaller loss of fuel due to methanolpermeation, resulting in smaller methanol supply required for satisfyingpower generation properties of a certain level. In addition, this allowsauxiliary facilities such as a fuel tank to be designed in a smallervolume, which can improve the energy density by weight and the energydensity by volume of a direct methanol fuel cell. Further, it ispreferable that the deterioration of performance due to the methanolpermeated can be suppressed.

Moreover, when a proton conducting polymer membrane of the presentinvention is compared with a membrane that has the same methanol barrierproperties and lower proton conductivity and in which the abovedescribed (A) and (B) are not satisfied, the membrane of the presentinvention can exhibit excellent power generation properties because ofsuperior proton conductivity of the membrane according to the presentinvention, in the case of supplying the same amount of methanol. Thisallows the membrane area and the number of cells that are required forobtaining necessary properties to be reduced. Preferably, this in turnallows a fuel cell body to be reduced in size and weight, thus allowingimprovement of the energy density by weight and the energy density byvolume of a direct methanol fuel cell.

In the present invention, the product of proton conductivity at 23° C.to an aqueous methanol solution of 10% by weight and a methanol barriercoefficient at 25° C. to an aqueous methanol solution of 10% by weightis 2.5×10⁻⁴ (S·day) /μmol or more. There is no specific upper limit tothe product, but it is preferably from 2.5×10⁻⁴ (S·day)/μmol to 2.5×10⁻¹(S·day)/μmol.

In addition, in the present invention, the product of protonconductivity at 23° C. to an aqueous methanol solution of 64% by weightand a methanol barrier coefficient at 25° C. to an aqueous methanolsolution of 64% by weight is 4.5×10⁻⁵ (S·day)/μmol or more. There is nospecific upper limit to the product, but it is preferably from 4.5×10⁻⁵(S·day)/μmol to 4.5×10⁻² (S·day)/μmol.

Furthermore, a proton conducting polymer membrane of the presentinvention preferably has an ion exchange capacity of 0.3milli-equivalent/g or more and has a crystalline phase. The protonconducting polymer membrane, when for example it contains a sulfonicacid group as a proton conducting substituent, refers to those whichhave a predetermined amount of sulfonic acid group mainly in anamorphous phase of a crystalline polymer and in which a crystallinephase derived from the above described crystalline polymer remains afterthe polymer is processed to a membrane form. When the ion exchangecapacity is lower than the above described range, the protonconductivity of a proton-conducting polymer membrane may be reduced.Known methods for determining the degree of crystallinity can be usedfor determining whether a proton-conducting polymer membrane of thepresent invention has a crystalline phase or not. For example, aspecific volume method (a density method), X-ray diffraction, aninfrared absorption spectra method, a nuclear magnetic resonance method(NMR), calorimetry or the like can be used. A proton-conducting polymermembrane of the present invention may be those in which crystallinepeaks can be proved by X-ray diffraction. Alternatively, the degree ofcrystallinity may be determined from melting endotherm orrecrystallization exotherm that can be measured by differential scanningcalorimetry (DSC) or differential thermal analysis (DTA) to prove thepresence or absence of a crystalline phase.

The degree of crystallinity of a proton-conducting polymer membrane ofthe present invention is not particularly limited, but it is preferablethat there remains about 5% of the saturated degree of crystallinityinherent in the crystalline hydrocarbon polymer composing thecrystalline polymer membrane. Further, it is more preferably that thereremain about 20% or more of the saturated degree of crystallinity. Whenthe degree of crystallinity is below 5% of the saturated degree ofcrystallinity, properties of a proton-conducting polymer membrane,particularly mechanical properties typified by tensile elongation andmethanol barrier properties, may be reduced to lower values than adesired value. For example, in the case of polyphenylene sulfide, thesaturated degree of crystallinity is 60%. For other crystalline polymersalso, it is possible to refer the values described in publicly knownliteratures.

A proton-conducting polymer membrane of the present inventionessentially contains in the membrane a substituent and/or a substancethat can conduct a proton. The substituent that can conduct a protonincludes a phosphoric acid group, a carboxylic acid group, a phenolichydroxy group or the like, other than the above described sulfonic acidgroup. Among these groups, a sulfonic acid group and/or a substituentcontaining a sulfonic acid group is preferred, in consideration ofeasiness of introducing a substituent and properties typified by theproton conductivity of a membrane obtained.

In the present invention, a sulfonic acid group refers to a sulfonicacid group represented by formula (1) and/or a substituent containing asulfonic acid group represented by formula (2):—SO₃H   (1)—R—SO₃H   (2)wherein R denotes a divalent organic group comprising at least one bondunit selected from a group consisting of alkylene, halogenated alkylene,arylene and halogenated arylene, or it may include an ether bond.

Moreover, a substance that can conduct a proton includes a stronglyacidic solution such as sulfuric acid and phosphoric acid, an inorganicoxide such as tungsten oxide hydrate (WO3.nH₂O) and molybdenum oxidehydrate (MoO₃.nH₂O) and an inorganic solid acid such astungstophosphoric acid molybdophosphoric acid.

A proton-conducting polymer membrane of the present invention preferablycomprises a hydrocarbon polymer in consideration of methanol barrierproperties and the like. Examples of the hydrocarbon polymer may includepolyacrylamide, polacrylonitrile, polyarylethersulfone, poly(allylphenyl ether), polyethylene oxide, polyetherethersulfone,polyetherketone, polyetherketoneketone, polyvinylchloride,poly(diphenylsiloxane), poly(diphenylphosphazene), polysulfone,polyparaphenylene, polyvinyl alcohol, poly(phenylglycidyl ether),poly(phenylmethylsiloxane), poly(phenylmethylphosphazene), polyphenyleneoxide, polyphenylene sulfoxide, polyphenylene sulfide sulfone,polyphenylene sulfone, polybenzimidazole, polybenzoxazole,polybenzothiazole, poly(α-methylstyrene), polystyrene,styrene-(ethylene-butylene)styrene copolymers,styrene-(polyisobutylene)-styrene copolymers,poly1,4-biphenyleneetherethersulfone, polyaryleneethersulfone,polyetherimide, cyanate resins, polyethylene, polypropylene, polyamide,polyacetal, polybutylene terephthalate, polyethylene terephthalate,syndiotactic polystyrene, polyphenylene sulfide, polyetheretherketone,polyethernitrile and the like. Among others, the hydrocarbon polymer ispreferably at least one selected from the group consisting ofpolybenzimidazole, polybenzoxazole, polybenzothiazole, polysulfone,polyetherethersulfone, polyarylethersulfone, polyphenylene sulfone,polyphenylene oxide, polyphenylene sulfoxide, polyphenylene sulfidesulfone, polyparaphenylene, polyetherketone, polyetherketoneketone,cyanate resins, polyethylene, polypropylene, polyamide, polyacetal,polybutylene terephthalate, polyethylene terephthalate, syndiotacticpolystyrene, polyphenylene sulfide, polyetheretherketone andpolyethernitrile, in consideration of easiness of introducing a sulfonicacid group and/or a substituent containing a sulfonic acid group andproperties of the membrane obtained such as proton conductivity,mechanical properties and chemical stability. Further, in the presentinvention, the hydrocarbon polymer is preferably a crystalline aromaticpolymer such as syndiotactic polystyrene, polyphenylene sulfide andpolyetheretherketone, in consideration of easiness of introducing asulfonic acid group and/or a substituent containing a sulfonic acidgroup and properties of the membrane obtained such as protonconductivity, mechanical properties, chemical stability, barrierproperties for fuel such as hydrogen and methanol, barrier propertiesfor oxidizers such as oxygen and air, and the like. Furthermore, thehydrocarbon polymer is more preferably polyphenylene sulfide since ithas high proton

conductivity, excellent mechanical properties and high methanol barrierproperties.

Polyphenylene sulfide of the present invention specifically comprisesrepeating-structural units represented by formula (3) below:—[Ar—S]_(n)—  (3)wherein Ar denotes a divalent aromatic unit represented by formulas (4)through (6) below; and n denotes an integer of 1 or more.

In addition, a part of Ar for the above described polyphenylene sulfidemay comprise any of the following structural units if necessary.

-   -   (1) An aromatic unit in which apart of hydrogen atoms thereof is        replaced with at least one substituent selected from the group        consisting of an alkyl group, a phenyl group, an alkoxy group, a        nitro group and a halogen group.    -   (2) A trifunctional phenyl sulfide unit.    -   (3) A crosslinking or a branch unit.

A proton conducting polymer membrane of the present invention preferablyhas an elongation at break according to JIS K 7127 of 10% or more, morepreferably 15% or more and most preferably 20% or more. When a protonconducting polymer membrane having an elongation at break of less than10% is used as an electrolyte, for example, in polymer electrolyte fuelcells or direct methanol fuel cells, the membrane may break because itcannot sufficiently follow a dimensional deformation due to the swellingthereof by absorbing water contained in a fuel or an oxidizer orproduced in the reaction. In order to set the elongation at break of aproton conducting polymer membrane in the above described range, itneeds to be appropriately set in consideration of the type of ahydrocarbon polymer or a crystalline aromatic polymer that is acomponent of the proton conducting polymer membrane, ion exchangecapacity required for allowing the membrane to exhibit desired protonconductivity and the like. It is basically necessary to manufacture aproton conducting polymer membrane in which ion exchange capacity isoptimized such that desired proton conductivity and elongation at breakare satisfied, since the higher the ion exchange capacity is, the lowerthe elongation at break tends to be.

A proton conducting polymer membrane of the present invention preferablyhas an ion exchange capacity of 0.3 milli-equivalent/g or more, morepreferably 0.5 milli-equivalent/g or more, most preferably 1.0milli-equivalent/g or more. A proton conducting polymer membrane havingan ion exchange capacity of less than 0.3 milli-equivalent/g is notpreferred, since it may not exhibit desired proton conductivity. Thereis no specific upper limit to the ion exchange capacity of a protonconducting polymer membrane of the present invention. However, the ionexchange capacity is preferably from 0.3 milli-equivalent/g to 0.5milli-equivalent/g.

A proton conducting polymer membrane of the present invention preferablyhas a proton conductivity at 23° C. of 1.0×10⁻³ S/cm or more, morepreferably 1.0×10⁻² S/cm or more. When the proton conductivity is lowerthan 1.0×10⁻³ S/cm, a proton conducting polymer membrane of the presentinvention may not exhibit adequate power generation properties in thecase of using it as an electrolyte membrane in a polymer electrolytefuel cell or a direct methanol fuel cell. There is no specific upperlimit to the proton conductivity at 23° C. of a proton conductingpolymer membrane of the present invention. However, the protonconductivity at 23° C. is preferably from 1.0×10⁻³ S/cm to 1.0 S/cm,more preferably from 1.0×10⁻² S/cm to 1.0 S/cm.

In order to set the proton conductivity of a proton conducting polymermembrane in the above described range, the amount of a proton conductingsubstituent such as a sulfonic acid group or a proton conductingsubstance may be controlled in consideration of the type of ahydrocarbon polymer or a crystalline aromatic polymer that is acomponent of the proton conducting polymer membrane.

A methanol barrier coefficient of a proton conducting polymer membraneof the present invention varies with the concentration of an aqueousmethanol solution used for measurement since the methanol barriercoefficient is not standardized with the methanol concentration. When anaqueous methanol solution of 64% by weight at 25° C. is used, themethanol barrier coefficient is preferably 3.0×10⁴ (cm·day)/μmol ormore, more preferably 5.0×10⁻⁴ (cm·day)/μmol or more, most preferably1.0×10⁻³ (cm·day)/μmol or more. In the case of using a proton conductingpolymer membrane, which has a methanol barrier coefficient of less than3.0×1- ⁻⁴ (cm·day)/μmol, as an electrolyte membrane in direct methanolfuel cells as described above, the membrane tends to exhibit degradationof performance caused by methanol permeation through the membrane. Aproton conducting polymer membrane of the present invention preferablyhas a methanol barrier coefficient at 25° C. to an aqueous methanolsolution of 64% by weight of 3.0×10⁻⁴ (cm·day)/μmol or more, and thereis no specific upper limit to it. However, the methanol barriercoefficient at 25° C. to an aqueous methanol solution of 64% by weightis more preferably from 3.0×10⁻⁴ (cm·day)/μmol to 3.0×10⁻¹(cm·day)/μmol.

In order to set the methanol permeation coefficient of a protonconducting polymer membrane in the above described range, it needs to beappropriately set in consideration of the type of a hydrocarbon polymeror a crystalline aromatic polymer that is a component of the protonconducting polymer membrane, ion exchange capacity required for allowingthe membrane to exhibit desired proton conductivity and the like. Theamount of a proton conducting substituent such as a sulfonic acid groupor a proton conducting substance may be basically controlled such thatdesired proton conductivity and a methanol permeation coefficient aresatisfied, since the higher the ion exchange capacity is, the lower themethanol barrier coefficient tends to be.

A proton conducting polymer membrane of the present invention ispreferably irradiated with at least one radiation selected from thegroup consisting of γ-ray, electron beam and ion beam. The protonconductivity tends to be improved by irradiating the above describedproton conducting polymer membrane with radiation to modify it. Methanolbarrier properties may also be improved. An electron beam isparticularly preferred in terms of a radiation dose, transmissionthrough a proton conducting polymer membrane, irradiation time(industrial continuous irradiation) and the like.

Irradiation atmosphere of the above described radiation may be selectedfrom any of air, a non-oxygen atmosphere and a vacuum atmosphere, butair is preferred in consideration of productivity. In the presentinvention, an atmosphere may be appropriately set in which theirradiation does not cause degradation of a proton conducting polymermembrane. In addition, irradiation atmosphere and a membrane may beheated in order to effectively perform modification of a protonconducting polymer membrane by irradiation. In this case also, acondition may be appropriately set in which the proton conductingpolymer membrane is not degraded.

Acceleration voltage of the above described radiation is preferably from0.01 MeV to 5.0 MeV. When the acceleration voltage is lower than 0.01MeV, the transmission of radiation through a proton conducting polymermembrane is reduced, and it tends to be difficult to obtain a membranethat is homogeneous throughout the membrane. Further, long irradiationis necessary in order to ensure a required irradiation dose, leading toconsiderable reduction in productivity. The acceleration voltageexceeding 5.0 MeV may require an apparatus which is larger thannecessary and may promote degradation of a proton conducting polymermembrane.

The irradiation dose of the above described radiation is preferably from10 kGy to 1,000 kGy. When the irradiation dose is less than 10 kGy,adequate irradiation effect may not be exhibited. When it exceeds 1,000kGy, there is a tendency that the irradiation effect is saturated;irradiation time is extended; and degradation and reduction ofproperties of a proton conducting polymer membrane is involved.

As for the thickness of a proton conducting polymer membrane of thepresent invention, any thickness may be selected depending onapplications. Thinner thickness is preferred in the range that themembrane has a practical mechanical strength in consideration ofreducing internal resistance of the membrane, and in the range that themembrane has barrier properties to fuel and an oxidizer when it is usedas an electrolyte membrane in a polymer electrolyte fuel cell. As forthe properties as an electrolyte membrane, the resistance value as amembrane is reduced with the reduction of the thickness of the membraneif ion exchange capacity and proton conductivity are the same.Therefore, the thickness of a membrane is preferably from 5 μm to 200μm, more preferably from 20 μm to 150 μm. When the thickness is lessthan 5 μm, there is a tendency that pin holes and a membrane fractureeasily occur in use. Further, when used as an electrolyte membrane inpolymer electrolyte fuel cells, barrier properties to fuel and anoxidizer may be insufficient, causing performance reduction.Furthermore, when used as an electrolyte membrane in direct methanolfuel cells, methanol barrier properties may be insufficient, causingperformance reduction due to methanol permeation. On the other hand,when the thickness exceeds 200 μm, the resistance of a proton conductingpolymer membrane may be increased, causing performance reduction.

Next, a membrane-electrode assembly of the present invention will bedescribed by illustrating the drawing as an example. FIG. 1 is asectional view of an essential part of a membrane-electrode assemblyusing a proton conducting polymer membrane of the present invention. Amembrane-electrode assembly 10 is composed of a proton conductingpolymer membrane 1, binder layers 2 and 3 formed on both sides of theproton conducting polymer membrane 1 as necessary, and catalyst loadedgas diffusion electrodes 8 and 9 having catalyst layers 4 and 5 anddiffusion layers 6 and 7, respectively, positioned outside the binderlayers. Catalyst loaded gas diffusion electrodes 8 and 9 may include,but not limited to, a commercially available catalyst loaded gasdiffusion electrode (for example, available from E-TEK, Inc., U.S.A).

In the present invention, a proton conducting polymer membrane of thepresent invention is used as the proton conducting polymer membrane 1.

The binder layers 2 and 3 may be the same or different, and maybe formedor may not be formed, as necessary. Typically, known proton conductingpolymers soluble in solvents are used such as perfluorocarbon sulfonicacid polymers typified by Nafion, sulfonated polyether ether ketones,sulfonated polyether sulfones, and sulfonated polyimides. These are usedfor joining (gluing) the proton conducting polymer membrane 1 to thecatalyst layers 4 and 5. These materials are required to have protonconductivity, chemical stability and the like similar to a protonconducting polymer membrane, in addition to joining properties thereofto different materials.

The catalyst layers 4 and 5 may be the same or different, and a catalystthat has the capability for oxidizing a fuel to be used (such ashydrogen or methanol) is used as one of the catalysts. As the othercatalyst, a catalyst having the capability for reducing a oxidizer to beused (such as oxygen or air) is used. Specifically, there are used thosein which a precious metal catalyst such as platinum is supported on aconductive material with a high surface area such as activated carbon,carbon nanohorns and carbon nanotubes. In the case of using othermaterials than pure hydrogen as a fuel, a composite or alloy catalystcomposed of platinum and ruthenium or the like is used in place ofplatinum in order to suppress the poisoning of a catalyst.

The diffusion layers 6 and 7 may be the same or different, and porousconductive materials such as carbon paper and carbon cloth are used asthe diffusion layers. These may be subjected to water-repellenttreatment with a fluorine compound such as polytetrafluoroethylene, ifnecessary, in order to prevent pores to be clogged with water that issupplied or produced in an electrochemical reaction. Typically, theabove described catalyst layers 4 and 5 are formed on these diffusionlayers 6 and 7 using, as a binder, known proton conducting polymerssoluble in solvents such as perfluorocarbon sulfonic acid polymerstypified by Nafion, sulfonated polyether ether ketones, sulfonatedpolyether sulfones, and sulfonated polyimides, preparing catalyst loadedgas diffusion electrodes 8 and 9 for use in the assembly.

In the membrane-electrode assembly 10 of the present invention, at leastone of the catalyst layers 4 and 5 preferably comprises a platinum andruthenium catalyst. In the present invention, a material with highmethanol barrier properties is preferably used as the proton conductingpolymer membrane 1, thereby capable of preventing methanol that remainsunreacted at one catalyst layer 4 from permeating through the protonconducting polymer membrane 1 to poison the catalyst in the othercatalyst layer 5.

A known or any other method can be selected as a method formanufacturing the membrane-electrode assembly 10 of the presentinvention. For example, an organic solvent solution of a component ofthe binders 2 and 3 is applied on the catalyst layers 4 and 5 of thecatalyst loaded gas diffusion electrodes 8 and 9, which are then placedon both surfaces of the proton conducting polymer membrane 1 afterremoving the solvent. Then, they can be subjected to hot pressingtypically at a pressing temperature of about 120° C. to 250° C. using apress machine such as a hot press machine or a roll press machine,preparing the membrane-electrode assembly 10. Further, if necessary, themembrane-electrode assembly 10 maybe prepared without using the binders2 and 3.

Next, a polymer electrode fuel cell (a direct methanol fuel cell) usinga proton conducting polymer membrane or a membrane-electrode assembly ofthe present invention will be described by illustrating the drawing asan example.

FIG. 2 is a sectional view of an essential part of a polymer electrolytefuel cell (a direct methanol fuel cell) using a proton conductingpolymer membrane or a membrane-electrode assembly of the presentinvention.

This is composed of the membrane-electrode assembly 10 of the presentinvention, separators 11 and 12 placed outside the assembly and channels13 and 14 formed in the separators for feeding a fuel gas or liquid andan oxidizer. A plate composed of carbon graphite or metal that haselectrical conductivity, chemical stability and barrier properties tofuel and oxidizers is used as the separators 11 and 12. Moreover, thesemaybe subjected to water-repellent treatment and corrosion-resistanttreatment, if necessary. The channels 13 and 14 for feeding a fuel gasor liquid and an oxidizer are formed on the surface of the separators 11and 13, composing a polymer electrode fuel cell (direct methanol fuelcell). The polymer electrode fuel cell is operated by feeding a gasessentially-composed of hydrogen, or a gas or a liquid essentiallycomposed of methanol into one channel 13, as a fuel gas or liquid, andfeeding a gas containing oxygen (oxygen or air) into the other channel14, as an oxidizer. When methanol is used as a fuel, the fuel cells aredirect methanol fuel cells.

A polymer electrolyte fuel cell (a direct methanol fuel cell) of thepresent invention can be used singly or by laminating a plurality offuel cells to form a stack, or can also form a fuel cell system in whichthese fuel cells are incorporated.

Further, a direct methanol fuel cell using a proton conducting polymermembrane of the present invention is described by illustrating thedrawing as an example.

FIG. 3 is a sectional view of an essential part of a direct methanolfuel cell comprising the proton conducting polymer membrane 1 or themembrane-electrode assembly 10 of the present invention. Themembrane-electrode assembly 10 is placed in a plane in required numberson both sides of a fuel (methanol or an aqueous methanol solution) tank15 that has the function to fill and feed a fuel (methanol or anaqueousmethanol solution). Further, on the outside of the membrane-electrodeassembly, there are placed supports 16 in which oxidizer channels 14 areformed. The membrane-electrode assemblies are sandwiched between thesupports to form cells and stacks of a direct methanol fuel cell.

Other than the above described examples, a proton conducting polymermembrane and a membrane-electrode assembly of the present invention canbe used as an electrolyte membrane and a membrane-electrode assembly indirect methanol fuel cells which are publicly known in Japanese PatentLaid-Open No. 2001-313046, No.2001-313047, NO.2001-93551, No.2001-93558,No. 2001-93561, No. 2001-102069, No. 2001-102070, No. 2001-283888, No.2000-268835, No. 2000-268836, No. 2001-283892 and the like.

Next, a method for manufacturing a proton conducting polymer membrane ofthe present invention will be described.

A method for manufacturing a proton conducting polymer membrane of thepresent invention comprises a method for manufacturing a protonconducting polymer membrane having a product ((S·day)/μmol) of protonconductivity (S/cm) at 23° C. and a methanol barrier coefficient((cm·day)/μmol) to an aqueous methanol solution of a specifiedconcentration at 25° C. that satisfies at least one of either (A) or (B)below, wherein

-   -   (A) the product in an aqueous methanol solution of 10% byweight        is 2.5×10⁻⁴ (S·day)/μmol or more, or    -   (B) the product in an aqueous methanol solution of 64% by weight        is 4.5×10⁻⁵ (S·day)/μmol or more,        the method preferably comprising bringing a film comprising a        hydrocarbon polymer into contact with a sulfonating agent.

Further, a method for manufacturing a proton conducting polymer membranethat has an ion exchange capacity of 0.3 milli-equivalent/g or more andhas a crystalline phase preferably comprises bringing a film comprisinga crystalline hydrocarbon polymer into contact with a sulfonating agent.Sulfonic acid groups are essentially introduced into an amorphous phase.This does not mean that no sulfonic acid groups are introduced into thecrystalline phase of a film comprising a crystalline hydrocarbonpolymer, but means that the crystalline phase remains in the film aftersulfonic acid groups are introduced.

As for the thickness of a film comprising the above describedhydrocarbon polymer or crystalline hydrocarbon polymer in the presentinvention, any thickness can be selected depending on applications.Thinner film thickness is preferred in consideration of introducing asulfonic acid group uniformly throughout a film and reducing an internalresistance of a proton conducting polymer membrane. On the other hand,the thickness of a film that is too thin is not preferred inconsideration of methanol barrier properties and handling properties. Inconsideration of the above, a film preferably has a thickness of from1.2 μm to 350 μm. When the above described film thickness is less than1.2 μm, manufacturing of the film is difficult, and there is a tendencythat handling properties deteriorate, for example, wrinkles or fractureoccurs during processing. When the thickness exceeds 350 μm, it isdifficult to uniformly sulfonate throughout the film, and the resultingproton conducting polymer membrane has a higher internal resistance,which may reduce the proton conductivity.

Known sulfonating agents can be used as the sulfonating agent, such aschlorosulfonic acid, oleum, sulfur trioxide, sulfur trioxide- triethylphosphate, concentrated sulfuric acid, trimethylsilyl chlorosulfate,trimethylbenzenesulfonic acid and the like. The sulfonating agent ispreferably at least one selected from the group consisting ofchlorosulfonic acid, oleum, sulfur trioxide and concentrated sulfuricacid, in consideration of industrial availability, easiness ofintroducing a sulfonic acid group and properties of the resulting protonconducting polymer membrane. Chlorosulfonic acid is more preferably usedparticularly in the present invention, because of easiness ofintroducing a sulfonic acid group, properties of the resulting membrane,industrial availability and the like.

Moreover, a method can be used in which a cyclic sulfur-containingcompound such as propane sultone or 1,4-butane sultone is brought intocontact with an aromatic unit in a hydrocarbon polymer in the presenceof a catalyst such as aluminum chloride according to the Friedel-Craftsreaction by optimizing the reaction system to introduce a substituentcomprising a sulfonic acid group such as a sulfopropyl group or asulfobutyl group.

Moreover, a proton conducting polymer membrane of the present inventionis preferably produced by contacting a film comprising the abovedescribed polymer with a sulfonating agent in the presence of a solvent.In the present invention, halides with three or more carbon atoms arepreferably used as the solvent. Since halides with three or more carbonatoms have higher boiling points and hardly evaporate compared withhalides with two or less carbon atoms such as dichloromethane and1,2-dichloroethane that are generally used for the sulfonation ofhydrocarbon compounds, use of these halides does not require auxiliaryfacilities for preventing evaporation of solvents or for recoveringsolvents evaporated, making it possible to reduce a production costinvolved in the auxiliary facilities. In addition, these solvents areeffective for maintaining methanol barrier properties of a resultingproton conducting polymer membrane at a certain level, and thus it ispossible to obtain a proton conducting polymer membrane with both highproton conductivity and high methanol barrier properties. In particular,when a film comprising a crystalline polymer such as polyphenylenesulfide is used, the film hardly deteriorates during the productionprocess, and preferably, it is possible to obtain a proton conductingpolymer membrane excellent in proton conductivity, methanol barrierproperties and mechanical properties.

When for example polyphenylene sulfide is used as a hydrocarbon polymer,examples of halides having three or more carbon atoms that can be usedin the present invention, in place of conventionally used halogenatedhydrocarbons having low carbon atoms such as dichloromethane and1,2-dichloroethane, may include 1-chloropropane, 1-bromopropane,1-iodopropane, 1-chlorobutane, 2-chlorobutane, 1-chloro-2-methylpropane,1-bromobutane, 2-bromobutane, 1-bromo-2-methylpropane, 1-iodobutane,2-iodobutane, 1-iodo-2-methylpropane, 1-chloropentane, 1-bromopentane,1-iodopentane, 1-chlorohexane, 1-bromohexane, 1-iodohexane,chlorocyclohexane, bromocyclohexane, iodocyclohexane and the like.

Particularly, in consideration of easiness in handling solvents to beused and properties of a proton conducting polymer membrane to beobtained, the above described solvent is preferably at least oneselected from the group consisting of 1-chloropropane, 1-bromopropane,1-chlorobutane, 2-chlorobutane, 1-chloro-2-methylpropane, 1-bromobutane,2-bromobutane, 1-bromo-2-methylpropane, 1-chloropentane, 1-bromopentane,1-chlorohexane, 1-bromohexane, chlorocyclohexane and bromocyclohexane.The solvent is more preferably at least one selected from1-chloropropane, 1-chlorobutane, 2-chlorobutane,1-chloro-2-methylpropane, 1-chloropentane, 1-chlorohexane andchlorocyclohexane, in terms of industrial availability. Among the abovedescribed solvents, 1-chlorobutane is preferred, in terms of industrialavailability and properties of a proton conducting polymer membrane tobe obtained.

The amount of usage of a sulfonating agent is preferably from 0.5 to 30equivalents, more preferably from 0.5 to 15 equivalents, relative to thearomatic unit in a hydrocarbon polymer. When the amount of usage of thesulfonating agent is less than 0.5 equivalent, there is a tendency thatthe amount of the sulfonic acid group to be introduced is reduced andthe time required for the introduction is extended. On the other hand,when the amount of usage of the sulfonating agent exceeds 30equivalents, there is a tendency that practical properties of a protonconducting polymer membrane are rather impaired; for example, a polymerfilm is chemically deteriorated, reducing the mechanical strength of aproton conducting polymer membrane to be obtained, which results in thedifficulty of handling of the membrane; and methanol barrier propertiesare reduced due to too much amount of introduction of a sulfonic acidgroup.

The concentration of a sulfonating agent in a solvent may beappropriately set in consideration of a target amount of introduction ofa sulfonic acid group and reaction conditions (temperature and time).Specifically, the concentration is preferably from 0.1% byweight to 10%by weight, more preferably from 0.2% by weight to 5% by weight. When theconcentration is lower than 0.1% by weight, the sulfonating agent ishardly brought into contact with the aromatic unit in a polymer. As aresult, there is a tendency that a sulfonic acid group may not beintroduced as desired, or it may take too much time to introduce thesulfonic acid group. On the other hand, when the concentration exceeds10% by weight, there is a tendency that the sulfonic acid group may beunevenly introduced, or a resultant proton conducting polymer membranemay have poor mechanical properties.

Moreover, although reaction temperature and reaction time for contactingthe above described ingredients are not particularly limited, thereaction temperature and reaction time are preferably set at a rangefrom 0° C. to 100° C., more preferably from 10° C. to 30° C., andpreferably set at 0.5 hour or more, more preferably from 2 hours to 100hours, respectively. When the reaction temperature is lower than 0° C.,it may be necessary to take some measures for facilities such ascooling, and the reaction time may tends to be too long. When thereaction temperature exceeds 100° C., there is a tendency that thereaction may proceed excessively, or a side-reaction may occur, reducingmembrane properties. Further, when the reaction time is less than 0.5hour, the contact of the sulfonating agent with the aromatic unit in apolymer may be insufficient, and so there is a tendency that a sulfonicacid group may not be introduced as desired. When the reaction timeexceeds 100 hours, there is a tendency that productivity is considerablyreduced, and that a large improvement in membrane properties cannot beexpected. In actuality, the reaction temperature and reaction time maybe set so that a proton conducting polymer membrane with desiredproperties can be effectively produced, in consideration of a reactionsystem such as a sulfonating agent and a solvent to be used, a targetproduction volume and the like.

A method for manufacturing a proton conducting polymer membrane of thepresent invention preferably comprises washing with water in order toremove an unreacted sulfonating agent and a solvent after the abovedescribed step for introducing a sulfonic acid group. At this time,preferably, a proton conducting polymer membrane after the step forintroducing a sulfonic acid group is not recovered, but is continuouslysubjected to washing followed by drying under a suitable condition toobtain the proton conducting polymer membrane. Alternatively, in placeof the washing with water, a proton conducting polymer membrane may beobtained by neutralization washing with an aqueous sodium hydroxidesolution or the like followed by acid treatment.

Moreover, in a method for manufacturing a proton conducting polymermembrane of the present invention, a sulfonating agent is preferablysulfur trioxide, and it is preferable that a film comprising ahydrocarbon polymer be brought into contact with a gas containing sulfurtrioxide to manufacture the proton conducting polymer membrane. In thiscase, the step for introducing a sulfonic acid group may involve drytreatment, in which solvent needs not be used for sulfonation, and sosteps and cost required for raw materials and regeneration treatment canbe reduced.

A method for manufacturing a proton conducting polymer membrane of thepresent invention may be performed continuously. Specifically, a filmcomprising a hydrocarbon polymer that is an object to be treated iscontinuously supplied to a reaction vessel in which it is reacted with asulfonating agent. Further, if necessary, a washing and drying steps maybe continuously performed without performing purification and recoveryof a proton conducting polymer membrane at a midpoint in the process.Productivity of the proton conducting polymer membrane will be improvedby this method.

In a method for manufacturing a proton conducting polymer membrane ofthe present invention, it is possible to introduce a sulfonic acid groupinto a polymer in a film (membrane) form by contacting a polymer filmwith a sulfonating agent in a reaction vessel. Therefore, in comparisonwith a conventional method in which a sulfonated polymer is synthesizedin a homogeneous reaction system and then processed into a membraneform, the method of the present invention can preferably omit steps suchas recovery, purification and drying of a reaction product, as well assteps such as dissolution of a sulfonated polymer into a solvent,application thereof on a support and removal of the solvent.Furthermore, the film is continuously supplied, thereby improving theproductivity of the same.

Moreover, peripheral equipment is prevented from corrosion due to asulfonating agent and poor film-handling properties due to a sulfonatingagent are improved, by performing the removal and washing of thesulfonating agent deposited and/or contained in the film immersed in areaction vessel. Conditions for the removal and washing may beappropriately set in consideration of the types of a sulfonating agentand hydrocarbon polymer to be used. Specifically, a remainingsulfonating agent maybe inactivated by washing with water, or may besubjected to neutralization treatment with alkali.

Moreover, a proton conducting polymer membrane can be recovered in apractically usable form by continuously drying the obtained protonconducting polymer membrane. The drying conditions may be appropriatelyset in consideration of the type of a polymer film to be used and theproperties of a proton conducting polymer membrane to be obtained. Sincea sulfonic acid group exhibits high hydrophilicity, the protonconducting polymer membrane may be considerably swelled with water inthe washing process. This may cause shrinkage during drying, leading toirregularities such as wrinkles and blisters. Therefore, at the time ofdrying, it is preferable that the proton conducting polymer membrane bedried under a suitable tension along the surface thereof. Alternatively,the membrane may be slowly dried under a controlled humidity in order toprevent quick drying.

Depending on a sulfonating agent to be used and reaction conditions forsulfonation, side reactions may occur. For example, when polyphenylenesulfide is used as a hydrocarbon polymer, a sulfide unit (—S—) in apolymer film may be oxidized to a sulfoxide unit (—SO—) or a sulfoneunit (—SO₂—); a sulfoxide unit (—SO—) may be oxidized to a sulfone unit(—SO₂—); or hydrogen in a phenylene unit may be replaced by asubstituent such as —Cl. However, a structural unit formed as a resultof the above described side reactions may be contained if it does notconsiderably reduce the properties of the resulting proton conductingpolymer membrane.

Furthermore, in a method for manufacturing a proton conducting polymermembrane of the present invention, the proton conducting polymermembrane prepared by the above described method is preferably irradiatedwith at least one radiation selected from the group consisting of γ-ray,electron beam and ion beam. Preferably, the dose of the radiation isfrom 10 kGy to 1,000 kGy.

In addition, when manufacturing a proton conducting polymer membranethat is manufactured according to a manufacturing method of the presentinvention, the polymer membrane may contain a suitable amount ofadditives such as plasticizers, antioxidants, antistatic agents,antibacterial agents, lubricants, surface active agents and variousfillers.

EXAMPLES

Hereinafter, the present invention will be more specifically describedwith reference to examples. However, the present invention is notlimited by these examples at all, and can be appropriately changedwithin the range that the gist thereof is not changed.

<Determination Method of Ion Exchange Capacity>

A proton conducting polymer membrane (about 10 mm×40 mm) is immersed in20 ml of a saturated aqueous sodium chloride solution at 25° C. to allowto them to react with each other at 60° C. for 3 hours in a water bath.They are cooled to 25° C.; the membrane is adequately washed withion-exchanged water; and all of the saturated aqueous sodium chloridesolution and the washing water are recovered. A phenolphthalein solutionis added as an indicator to the solution recovered, which is subjectedto neutralization titration with a 0.01 N aqueous sodium hydroxidesolution, for calculating ion exchange capacity.

<Determination Method of Proton Conductivity>

A proton conducting polymer membrane (about 10 mm×40 mm) stored inion-exchange water is taken out, and water on the surface of themembrane is wiped off with filter paper. The membrane was mounted on aTeflon (registered trade mark) cell of a bielectrode non-enclosedsystem, and a platinum electrode was mounted on the surface (the sameside) of the membrane such that the distance between electrodes is 30mm. The resistance of the membrane at 23° C. is measured by analternating current impedance method (frequency: from 42 Hz to 5 MHz,applied voltage: 0.2 V) to calculate the proton conductivity.

<Determination Method of Methanol Barrier Properties>

Ion-exchanged water and an aqueous methanol solution of a specifiedconcentration are separated with a proton conducting polymer membraneusing a membrane permeation experimental apparatus available from VidrexCompany Limited in a 25° C. environment. After a lapse of predeterminedtime, the solution that contains methanol permeated to the side ofion-exchanged water is collected, and the methanol content in thesolution is quantified by a gas chromatograph. The permeation speed ofmethanol is determined from the result of the quantification, which isused for calculating the methanol permeation coefficient and themethanol barrier coefficient. The methanol permeation coefficient andthe methanol barrier coefficient are calculated according tomathematical expressions 1 and 2 below.Methanol permeation coefficient (μmol/(cm·day))=amount of methanolpermeated (μmol)×film thickness (cm)/(area of membrane (cm²)×permeationtime (day))   [Mathematical expression [1]Methanol barrier coefficient ((cm·day)/μmol)=1/(methanol permeationcoefficient (μmol/(cm·day))   [Mathematical expression [2]<Determination Method of Mechanical Properties (Breaking Strength andElongation at Break)>

Breaking strength and elongation at break of a proton conducting polymermembrane are determined according to a method of JIS K 7127. Fivesamples (n=5) of a proton conducting polymer membrane (width: about 10mm) are used to determine mechanical properties at conditions of adistance between chucks of 30 mm and a rate of pulling of 20 mm/min. Asfor elongation at break, the average value and the maximum value arerecorded.

<Dimensional Stability>

Points of measurement with a space of about 20 mm are marked at thecentral part of a proton conducting polymer membrane (about 40 mm×10mm). The membrane is immersed in ion-exchanged water or in an aqueousmethanol solution of 64% by weight for two hours in a 25° C.environment. Subsequently, the distance between the points ofmeasurement is measured to calculate a percent dimensional change.

<Determination Method of X-Ray Diffraction>

X-ray diffraction of a proton conducting polymer membrane is determinedusing an X-ray diffraction apparatus available from Shimadzu Corporationat conditions of the X-ray to be used of Cu.Kα ray, an X-ray intensityof 30 kV and 100 A, an angle region of 2θ=5−50 and a scanning speed of 2/min.

<Crystallinity>

The presence or absence of crystallinity is determined according to thestandard described below, from the X-ray diffraction patterns obtainedby the above described X-ray diffraction determination:

-   -   Yes: A sharp peak can be recognized by the X-ray diffraction        determination.    -   No: A sharp peak cannot be recognized by the X-ray diffraction        determination.

Example 1

Polyphenylene sulfide was used as a hydrocarbon polymer.

To a glass vessel, 729 g of 1-chlorobutane and 3.65 g of chlorosulfonicacid were weighed to prepare a chlorosulfonic acid solution. Apolyphenylene sulfide film (trade name: Torelina, thickness: 50 μm,available from Toray Industries, Inc.) was weighed in an amount of 1.69g, immersed in the chlorosulfonic acid solution and left standing atroom temperature for 20 hours (chlorosulfonic acid was added in anamount of 2 equivalents relative to the aromatic unit of thepolyphenylene sulfide). After left standing at room temperature for 20hours, the polyphenylene sulfide film was recovered and washed withion-exchanged water until it is neutralized.

A polyphenylene sulfide film after washing was left standing under acontrolled relative humidity of 98%, 80%, 60% or 50% for 30 minutes in athermo-hygrostat at 23° C. to dry the film, obtaining a polyphenylenesulfide membrane in which a sulfonic acid group is introduced(hereinafter referred to as a sulfonated polyphenylene sulfide membrane)(80 mm×80 mm, thickness: 51 μm), as a proton conducting polymermembrane.

Various properties of these proton conducting polymer membranes weredetermined according to the methods as described above.

The results of the evaluation of the properties of this membrane areshown in Tables 1 to 5 and in FIG. 4.

Example 2

This example was performed in the same manner as in Example 1 exceptthat 721 g of 1-chlorobutane, 5.40 g of chlorosulfonic acid and 1.67 gof the polyphenylene sulfide film were used (chlorosulfonic acid wasadded in an amount of 3 equivalents relative to the aromatic unit of thepolyphenylene sulfide). It was observed that the resulting sulfonatedpolyphenylene sulfide membrane (80 mm×80 mm, thickness: 53 μm)maintained the shape of a membrane.

The results of the evaluation of the properties of this membrane areshown in Tables 1 to 3 and in FIG. 5.

Example 3

This example was performed in the same manner as in Example 1 exceptthat 716 g of 1-chlorobutane, 7.16 g of chlorosulfonic acid and 1.66 gof the polyphenylene sulfide film were used (chlorosulfonic acid wasadded in an amount of 4 equivalents relative to the aromatic unit of thepolyphenylene sulfide). It was observed that the resulting sulfonatedpolyphenylene sulfide membrane (80 mm×80 mm, thickness: 54 μm)maintained the shape of a membrane.

The results of the evaluation of the properties of this membrane areshown in Tables 1, 2 and 5 and in FIG. 6.

Example 4

This example was performed in the same manner as in Example 1 exceptthat 734 g of 1-chlorobutane, 11.00 g of chlorosulfonic acid and 1.70 gof the polyphenylene sulfide film were used (chlorosulfonic acid wasadded in an amount of 6 equivalents relative to the aromatic unit of thepolyphenylene sulfide). It was observed that the resulting sulfonatedpolyphenylene sulfide membrane (80 mm×80 mm, thickness: 78 μm)maintained the shape of a membrane.

The results of the evaluation of the properties of this membrane areshown in Tables 1 to 3.

Example 5

This example was performed in the same manner as in Example 1 exceptthat 746 g of 1-chlorobutane, 14.93 g of chlorosulfonic acid and 1.73 gof the polyphenylene sulfide film were used (chlorosulfonic acid wasadded in an amount of 8 equivalents relative to the aromatic unit of thepolyphenylene sulfide). It was observed that the resulting sulfonatedpolyphenylene sulfide membrane (80 mm×80 mm, thickness: 93 μm)maintained the shape of a membrane.

The results of the evaluation of the properties of this membrane areshown in Tables 1 to 3.

Example 6

This example was performed in the same manner as in Example 1 exceptthat 712 g of 1-chlorobutane, 17.80 g of chlorosulfonic acid and 1.65 gof the polyphenylene sulfide film were used (chlorosulfonic acid wasadded in an amount of 10 equivalents relative to the aromatic unit ofthe polyphenylene sulfide). It was observed that the resultingsulfonated polyphenylene sulfide membrane (80mm×80 mm, thickness: 100μm) maintained the shape of a membrane.

The results of the evaluation of the properties of this membrane areshown in Tables 1 to 3.

Example 7

This example was performed in the same manner as in Example 1 exceptthat 583 g of 1-chlorobutane, 5.83 g of chlorosulfonic acid and 1.35 gof a polyphenylene sulfide film (trade name: Torelina, thickness: 25 μm,available from Toray Industries, Inc.) were used (chlorosulfonic acidwas added in an amount of 4 equivalents relative to the aromatic unit ofthe polyphenylene sulfide). It was observed that the resultingsulfonated polyphenylene sulfide membrane (80 mm×80 mm, thickness: 32μm) maintained the shape of a membrane.

The results of the evaluation of the properties of this membrane areshown in Tables 1 and 2.

Example 8

This example was performed in the same manner as in Example 7 exceptthat 595 g of 1-chlorobutane, 7.44 g of chlorosulfonic acid and 1.38 gof the polyphenylene sulfide film were used (chlorosulfonic acid wasadded in an amount of 5 equivalents relative to the aromatic unit of thepolyphenylene sulfide). It was observed that the resulting sulfonatedpolyphenylene sulfide membrane (80 mm×80 mm, thickness: 35 μm)maintained the shape of a membrane.

The results of the evaluation of the properties of this membrane areshown in Tables 1 and 2.

Example 9

This example was performed in the same manner as in Example 7 exceptthat 578 g of 1-chlorobutane, 8.67 g of chlorosulfonic acid and 1.34 gof the polyphenylene sulfide film were used (chlorosulfonic acid wasadded in an amount of 6 equivalents relative to the aromatic unit of thepolyphenylene sulfide). It was observed that the resulting sulfonatedpolyphenylene sulfide membrane (80 mm×80 mm, thickness: 40 μm)maintained the shape of a membrane.

The results of the evaluation of the properties of this membrane areshown in Tables 1 to 3.

Example 10

This example was performed in the same manner as in Example 7 exceptthat 587 g of 1-chlorobutane, 11.74 g of chlorosulfonic acid and 1.36 gof the polyphenylene sulfide film were used (chlorosulfonic acid wasadded in an amount of 8 equivalents relative to the aromatic unit of thepolyphenylene sulfide). It was observed that the resulting sulfonatedpolyphenylene sulfide membrane (80 mm×80 mm, thickness: 42 μm)maintained the shape of a membrane.

The results of the evaluation of the properties of this membrane areshown in Tables 1 to 3.

Example 11

A sulfonated polyphenylene sulfide membrane obtained according toExample 4 was irradiated with an electron beam of an accelerationvoltage of 4.6 MeV, an irradiation dose of 500 kGy and an electriccurrent of 20 mA. It was observed that the resulting sulfonatedpolyphenylene sulfide membrane (80 mm×80 mm, thickness: 83 μm)maintained the shape of a membrane.

The results of the evaluation of the properties of this membrane areshown in Tables 1 and 2.

Example 12

This example was performed in the same manner as in Example 11 exceptthat the sulfonated polyphenylene sulfide membrane obtained according toExample 5 was used in place of the sulfonated polyphenylene sulfidemembrane obtained in Example 4. It was observed that the resultingsulfonated polyphenylene sulfide membrane (80 mm×80 mm, thickness: 93μm) maintained the shape of a membrane.

The results of the evaluation of the properties of this membrane areshown in Tables 1 to 3.

Example 13

This example was performed in the same manner as in Example 11 exceptthat the sulfonated polyphenylene sulfide membrane obtained according toExample 6 was used in place of the sulfonated polyphenylene sulfidemembrane obtained in Example 4. It was observed that the resultingsulfonated polyphenylene sulfide membrane (80 mm×80 mm, thickness: 104μm) maintained the shape of a membrane.

The results of the evaluation of the properties of this membrane areshown in Tables 1 and 2.

Example 14

This example was performed in the same manner as in Example 11 exceptthat the sulfonated polyphenylene sulfide membrane obtained according toExample 8 was used in place of the sulfonated polyphenylene sulfidemembrane obtained in Example 4. It was observed that the resultingsulfonated polyphenylene sulfide membrane (80 mm×80 mm, thickness: 36μm) maintained the shape of a membrane.

The results of the evaluation of the properties of this membrane areshown in Tables 1 to 3.

Example 15

This example was performed in the same manner as in Example 11 exceptthat the sulfonated polyphenylene sulfide membrane obtained according toExample 9 was used in place of the sulfonated polyphenylene sulfidemembrane obtained in Example 4. It was observed that the resultingsulfonated polyphenylene sulfide membrane (80 mm×80 mm, thickness: 41μm) maintained the shape of a membrane.

The results of the evaluation of the properties of this membrane areshown in Tables 1 to 3.

Example 16

This example was performed in the same manner as in Example 11 exceptthat the sulfonated polyphenylene sulfide membrane obtained according toExample 10 was used in place of the sulfonated polyphenylene sulfidemembrane obtained in Example 4. It was observed that the resultingsulfonated polyphenylene sulfide membrane (80 mm×80 mm, thickness: 48μm) maintained the shape of a membrane.

The results of the evaluation of the properties of this membrane areshown in Tables 1 to 3.

Example 17

To a glass container of 500 mL, 1.0 g of a polyphenylene sulfide film(tradename: Torelina, thickness: 50 μm, available from Toray Industries,Inc.) was weighed, and 1.5 g of a sulfur trioxide solution was addeddropwise from a dropping funnel. They were warmed up to 60° C. with awater bath to evaporate sulfur trioxide to bring it into contact withthe polyphenylene sulfide film. They were left standing in this statefor 30 minutes, and the polyphenylene sulfide film was washed withion-exchanged water until it is neutralized.

A polyphenylene sulfide film after washing was left standing under acontrolled relative humidity of 98%, 80%, 60% or 50% for 30 minutes in athermo-hygrostat at 23° C. to dry the film, obtaining a polyphenylenesulfide membrane in whichasulfonic acid group is introduced (hereinafterreferred to as a sulfonated polyphenylene sulfide membrane) (50 mm×50mm, thickness: 70 μm), as a proton conducting polymer membrane.

The results of the evaluation of the properties of this membrane areshown in Tables 1, 2 and 5 and in FIG. 7.

Comparative Example 1

A Nafion 115 film available from EI du Pont de Nemours and Company wasused as a sulfonic acid group-containing membrane comprising anon-hydrocarbon polymer.

The results of the evaluation of the properties of this membrane areshown in Tables 1, 2 and 4.

Comparative Example 2

In a separable flask of 500 mL, 15 g of 1,4-polyphenylene sulfide(number average molecular weight: 10,000, available from AldrichCorporation) was dissolved in 300 mL of chlorosulfonic acid. The mixturewas cooled with ice and stirred at a reaction temperature of 5° C. for60 minutes. Then, to the reaction mixture maintained at 20° C., 100 mLof oleum (15% SO₃) was added dropwise, and the resulting mixture wasstirred for 300 minutes to react 1,4-polyphenylene sulfide with oleum.The resulting reaction solution was added to a mixture of 2 kg of iceand 600 mL of sulfuric acid (30% by weight) with stirring. A precipitatewas washed in boiling ion-exchanged water until the washing water isneutral, by exchanging ion-exchanged water (exchanging ion-exchangedwater 10 times, total washing time of 80 hours). The precipitate wasrecovered by filtration followed by drying at 80° C. for 3 hours toobtain a sulfonated polyphenylene sulfide.

A 20% by weight solution of the obtained sulfonated polyphenylenesulfide in N-methyl-2-pyrolidone was prepared, cast on a glass dish anddried under reduced pressure at 150° C. However, a self-supporting shapeof a membrane was not obtained, and it was unable to perform theevaluation of the properties other than ion exchange capacity.

The result of the evaluation of the properties of this membrane is shownin Tables 1.

Comparative Example 3

In a mayonnaise bottle of 900 mL, 945 g of dichloromethane and 4.72 g ofchlorosulfonic acid were weighed to prepare a chlorosulfonic acidsolution. Then, 2.21 g of a polyphenylene sulfide film (tradename:Torelina, thickness: 50 μm, available from Toray Industries, Inc.) wasweighed and immersed in the chlorosulfonic acid solution to be broughtinto contact with the solution. In this state, they were left standingat room temperature for 20 hours (chlorosulfonic acid was added in anamount of 2 equivalents relative to the aromatic unit of thepolyphenylene sulfide). After left standing at room temperature for 20hours, the polyphenylene sulfide film was recovered and washed withion-exchanged water until it is neutralized.

A polyphenylene sulfide film after washing was left standing under acontrolled relative humidity of 98%, 80%, 60% or 50% for 30 minutes in athermo-hygrostat at 23° C. to dry the film, obtaining a polyphenylenesulfide membrane in which a sulfonic acid group is introduced(hereinafter referred to as a sulfonated polyphenylene sulfide membrane)(50 mm×50 mm, thickness: 110 μm), as a proton conducting polymermembrane.

The results of the evaluations of the properties of this membrane areshown in Tables 1 to 5 and in FIG. 8.

Comparative Example 4

To 100 parts by weight of a polyphenylene sulfide (trade name: DIC-PPSFZ-2200-A5, available from Dainippon Ink and Chemicals, Incorporated), 2parts by weight of tricresyl phosphate (trade name: TCP, available fromDaihachi Chemical Industry Co., Ltd.) was added as a plasticizer. Theywere melted and mixed in a twin-screw extruder heated at 280° C. toobtain a pellet composed of a predetermined mixture. The pellet wasmelt-extruded in an extruder having a screw temperature of 290° C. and aT-die temperature of 320° C. to obtain a film with a thickness of 50 μm.

To a mayonnaise bottle of 900 mL, 945 g of dichloromethane and 4.72 g ofchlorosulfonic acid were weighed to prepare a chlorosulfonic acidsolution. Then, 2.21 g of a film composed of the polyphenylene sulfideobtained in the above described method was weighed and immersed in thechlorosulfonic acid solution to be brought into contact with thesolution. In this state, they were left standing at room temperature for20 hours (chlorosulfonic acid was added in an amount of 2 equivalentsrelative to the aromatic unit of the polyphenylene sulfide). After leftstanding at room temperature for 20 hours, the polyphenylene sulfidefilm was recovered and washed with ion-exchanged water until it isneutralized.

A polyphenylene sulfide film after washing was left standing under acontrolled relative humidity of 98%, 80%, 60% or 50% for 30 minutes in athermo-hygrostat at 23° C. to dry the film, obtaining a polyphenylenesulfide membrane in which a sulfonic acid group is introduced(hereinafter referred to as a sulfonated polyphenylene sulfide membrane)(80 mm×80 mm, thickness: 60 μm), as a proton conducting polymermembrane.

The results of the evaluations of the properties of this membrane areshown in Tables 1 to 5 and in FIG. 9. TABLE 1 Ion Exchange capacity andproton conductivity of proton conducting polymer membranes Ion Exchangecapacity Proton conductivity (milli-equivalent/g) (S/cm) Example 1 0.52.8 × 10⁻² Example 2 1.0 2.4 × 10⁻² Example 3 1.1 3.7 × 10⁻² Example 41.3 4.5 × 10⁻² Example 5 1.5 3.6 × 10⁻² Example 6 1.8 7.0 × 10⁻² Example7 1.2 1.7 × 10⁻² Example 8 1.2 2.8 × 10⁻² Example 9 1.5 4.8 × 10⁻²Example 10 1.6 5.3 × 10⁻² Example 11 1.4 2.7 × 10⁻² Example 12 1.8 5.0 ×10⁻² Example 13 2.1 7.2 × 10⁻² Example 14 1.7 3.7 × 10⁻² Example 15 1.84.9 × 10⁻² Example 16 2.0 6.2 × 10⁻² Example 17 0.9 2.5 × 10⁻²Comparative Example 1 0.9 5.8 × 10⁻² Comparative Example 2 1.6 —Comparative Example 3 1.5 7.7 × 10⁻² Comparative Example 4 1.5 6.5 ×10⁻²

TABLE 2 Methanol barrier coefficient, and the product of protonconductivity and methanol barrier coefficient, of proton conductivepolymer membranes Product of proton conductivity and methanol Methanolbarrier coefficient ((cm · day)/μmol) barrier coefficient ((S ·day)/μmol) 3.2 wt % 10 wt % 13.3 wt % 27.5 wt % 64 wt % 3.2 wt % 10 wt %13.3 wt % 27.5 wt % 64 wt % Example 1 — >10⁻¹ — — >10⁻¹ — >2.8 × 10⁻³  — — >2.8 × 10⁻³   Example 2 — — — — >10⁻¹ — — — — >2.4 × 10⁻³   Example3 — — — — 1.6 × 10⁻² — — — — 5.9 × 10⁻⁴ Example 4 1.3 × 10⁻¹ 2.6 × 10⁻²2.5 × 10⁻² 1.1 × 10⁻² 5.4 × 10⁻³ 5.9 × 10⁻³ 1.2 × 10⁻³ 1.1 × 10⁻³ 5.0 ×10⁻⁴ 2.4 × 10⁻⁴ Example 5 3.2 × 10⁻² 8.9 × 10⁻³ 7.3 × 10⁻³ 3.6 × 10⁻³8.4 × 10⁻⁴ 1.2 × 10⁻³ 3.2 × 10⁻⁴ 2.6 × 10⁻⁴ 1.3 × 10⁻⁴ 3.0 × 10⁻⁵Example 6 — 5.2 × 10⁻³ — — 8.9 × 10⁻⁴ — 3.6 × 10⁻⁴ — — 6.2 × 10⁻⁵Example 7 — — — — 2.3 × 10⁻² — — — — 3.9 × 10⁻⁴ Example 8 — 3.4 × 10⁻² —— 7.4 × 10⁻³ — 9.5 × 10⁻⁴ — — 2.1 × 10⁻⁴ Example 9 2.5 × 10⁻² 7.6 × 10⁻³5.7 × 10⁻³ 3.6 × 10⁻³ 1.1 × 10⁻³ 1.2 × 10⁻³ 3.6 × 10⁻⁴ 2.7 × 10⁻⁴ 1.7 ×10⁻⁴ 5.3 × 10⁻⁵ Example 10 — — — — 8.6 × 10⁻⁴ — — — — 4.6 × 10⁻⁵ Example11 7.1 × 10⁻² 3.0 × 10⁻² 2.0 × 10⁻² 1.2 × 10⁻² 2.9 × 10⁻³ 1.9 × 10⁻³ 8.1× 10⁻⁴ 5.4 × 10⁻⁴ 3.2 × 10⁻⁴ 7.8 × 10⁻⁵ Example 12 1.9 × 10⁻² 7.4 × 10⁻³5.3 × 10⁻³ 3.3 × 10⁻³ 1.1 × 10⁻³ 9.5 × 10⁻⁴ 3.7 × 10⁻⁴ 2.7 × 10⁻⁴ 1.7 ×10⁻⁴ 5.5 × 10⁻⁵ Example 13 1.2 × 10⁻² 3.9 × 10⁻³ 3.6 × 10⁻³ 1.4 × 10⁻³6.6 × 10⁻⁴ 8.6 × 10⁻⁴ 2.8 × 10⁻⁴ 2.6 × 10⁻⁴ 1.0 × 10⁻⁴ 4.8 × 10⁻⁵Example 14 4.3 × 10⁻² 2.2 × 10⁻² 1.4 × 10⁻² 8.0 × 10⁻³ 3.0 × 10⁻³ 1.6 ×10⁻³ 8.1 × 10⁻⁴ 5.2 × 10⁻⁴ 3.0 × 10⁻⁴ 1.1 × 10⁻⁴ Example 15 3.2 × 10⁻²1.4 × 10⁻² 1.0 × 10⁻² 4.8 × 10⁻³ 1.8 × 10⁻³ 1.6 × 10⁻³ 6.9 × 10⁻⁴ 4.9 ×10⁻⁴ 2.4 × 10⁻⁴ 8.8 × 10⁻⁵ Example 16 1.7 × 10⁻² 6.7 × 10⁻³ 3.9 × 10⁻³2.3 × 10⁻³ 8.2 × 10⁻⁴ 1.1 × 10⁻³ 4.2 × 10⁻⁴ 2.4 × 10⁻⁴ 1.4 × 10⁻⁴ 5.1 ×10⁻⁵ Comparative 9.2 × 10⁻³ 2.3 × 10⁻³ 1.4 × 10⁻³ 7.4 × 10⁻⁴ 2.4 × 10⁻⁴5.3 × 10⁻⁴ 1.3 × 10⁻⁴ 8.7 × 10⁻⁵ 4.3 × 10⁻⁵ 1.4 × 10⁻⁵ Example 1Comparative — 2.6 × 10⁻³ — — 3.8 × 10⁻⁴ — 2.0 × 10⁻⁴ — — 2.9 × 10⁻⁵Example 3 Comparative — 3.7 × 10⁻³ — — 5.2 × 10⁻⁴ — 2.4 × 10⁻⁴ — — 4.1 ×10⁻⁵ Example 4

TABLE 3 Mechanical properties of proton conducting polymer membranesBreaking Elongation at Elongation at strength break (average) break(maximum) (MPa) (%) (%) Example 1 145 40 52 Example 2 83 20 24 Example 462 16 23 Example 5 59 12 16 Example 6 60 17 25 Example 9 57 20 41Example 10 55 18 29 Example 12 63 12 17 Example 14 59 25 52 Example 1557 17 30 Example 16 55 15 22 Comparative Example 3 51 9 12 ComparativeExample 4 38 11 20

TABLE 4 Percent dimensional change of proton conducting polymermembranes Percent dimensional change (%) Ion-Exchanged Methanol of 64%water by weight Example 1 0 0.4 Comparative Example 1 12 44 ComparativeExample 3 10 20 Comparative Example 4 9 22

TABLE 5 Crystallinity of proton conducting polymer membraneCrystallinity Example 1 exist Example 2 exist Example 3 exist Example 17exist Comparative Example 3 virtually not exist Comparative Example 4virtually not exist

When Examples 1 to 17 are compared with Comparative Examples 1, 3 and 4,in Tables 1 to 5, it is apparent that proton conducting polymermembranes of the present invention have proton conductivity of the sameorder as that of conventional proton conducting polymer membranes andare useful as the electrolytes in polymer electrolyte fuel cells anddirect methanol fuel cells. In addition, it is apparent that protonconducting polymer membranes of the present invention have bettermethanol barrier coefficients than conventional proton conductingpolymer membranes and are useful as the electrolytes in direct methanolfuel cells. Furthermore, it is shown that proton conducting polymermembranes of the present invention each have a larger product of protonconductivity and a methanol barrier coefficient as compared withconventional proton conducting polymer membranes and havecharacteristics that proton conductivity and methanol barrier propertiesare compatible. Accordingly, it is apparent that proton conductingpolymer membranes of the present invention are useful as the electrodesin direct methanol fuel cells.

When Examples 1, 2, 4 to 6, 9, 10, 12, and 14 to 16 are compared withComparative Examples 3 and 4, in Table 3, it is apparent that protonconducting polymer membranes of the present invention have betterbreaking strength and elongation at break than conventional protonconducting polymer membranes and are useful as the electrolytes inpolymer electrolyte fuel cells and direct methanol fuel cells.

When Example 1 is compared with Comparative Examples 1, 3 and 4, inTable 4, it is shown that a proton conducting polymer membrane of thepresent invention has higher dimensional stability to ion-exchangedwater and an aqueous methanol solution of 64% by weight and betterhandling properties than conventional proton conducting polymermembranes.

Accordingly, it is apparent that a proton conducting polymer membrane ofthe present invention is useful as the electrode in polymer electrolytefuel cells and direct methanol fuel cells.

From the results of the evaluations of X-ray diffraction in FIGS. 4 to 9and crystallinity in Table 5, it is apparent that proton conductingpolymer membranes of the present invention in Examples 1 to 3 and 17each have a crystalline peak, showing that a crystalline phase remains.On the other hand, from the results of the determination of X-raydiffraction in FIGS. 8 and 9, it is apparent that no crystalline peak isobserved in conventional proton conducting polymer membranes inComparative Examples 3 and 4, showing that almost no crystalline phaseremains.

Moreover, although a conventional proton conducting polymer membrane inComparative Example 2 cannot provide a self-supporting membrane shape aswell as it takes as long as 90 hours to manufacture the same, a protonconducting polymer membrane of the present invention in Example 1 can bemanufactured in about 24 hours, showing that the present invention isalso excellent in terms of productivity. That is to say, themanufacturing method of the present invention can provide a protonconducting polymer membrane having practical handling properties in asimpler method.

INDUSTRIAL APPLICABILITY

According to the present invention, it has become possible thatexcellent proton conductivity and high methanol barrier properties canbe exhibited by a proton conducting polymer membrane having a product ofproton conductivity and a methanol barrier coefficient of a specificvalue or more, or a proton conducting polymer membrane having an ionexchange capacity of 0.3 milli-equivalent/g or more, and having acrystalline phase.

These proton conducting polymer membranes have excellent protonconductivity, high methanol barrier properties, excellent mechanicalproperties and the like, and are useful as the electrodes in polymerelectrode fuel cells and direct methanol fuel cells.

1. A proton conducting polymer membrane having a product ((S·day)/μmol)of a proton conductivity (S/cm) at 23° C. and a methanol barriercoefficient ((cm·day)/μmol) at 25° C. in an aqueous methanol solution ofa specified concentration that satisfies at least one of either (A) or(B) below, wherein (A) the product in an aqueous methanol solution of10% by weight is 2.5×10⁻⁴ (S·day)/μmol or more, or (B) the product in anaqueous methanol solution of 64% by weight is 4.5×10⁻⁵ (S·day)/μmol ormore.
 2. A proton conducting polymer membrane having an ion exchangecapacity of 0.3 milli-equivalent/g or more, and having a crystallinephase.
 3. The proton conducting polymer membrane according to claim 1 or2, wherein the proton conducting polymer membrane comprises sulfonicacid groups.
 4. The proton conducting polymer membrane according toclaim 1 or 2, wherein the proton conducting polymer membrane comprises ahydrocarbon polymer.
 5. The proton conducting polymer membrane accordingto claim 4, wherein the hydrocarbon polymer comprises a crystallinearomatic polymer.
 6. The proton conducting polymer membrane according toclaim 5, wherein the crystalline aromatic polymer is polyphenylenesulfide.
 7. The proton conducting polymer membrane according to claim 1or 2, wherein the proton conducting polymer membrane has an elongationat break of 10% or more as determined according to JIS K
 7127. 8. Theproton conducting polymer membrane according to claim 1 or 2, whereinthe proton conducting polymer membrane has a proton conductivity of1.0×10⁻³ S/cm or more at 23° C.
 9. The proton conducting polymermembrane according to claim 8, wherein the proton conducting polymermembrane has a proton conductivity of 1.0×10⁻² S/cm or more at 23° C.10. The proton conducting polymer membrane according to claim 1 or 2,wherein the proton conducting polymer membrane has a methanol barriercoefficient of 3.0×10⁻⁴ (cm·day)/μmol or more at 25° C. in an aqueousmethanol solution by 64% by weight.
 11. The proton conducting polymermembrane according to claim 1 or 2, wherein the proton conductingpolymer membrane is irradiated with at least one radiation selected fromthe group consisting of γ-ray, electron beam and ion beam.
 12. Theproton conducting polymer membrane according to claim 11, wherein thedose of the radiation is from 10 kGy to 1,000 kGy.
 13. Amembrane-electrode assembly using the proton conducting polymer membraneaccording to claim
 1. 14. The membrane-electrode assembly according toclaim 13, wherein at least one catalyst layer of the membrane-electrodeassembly comprises a platinum and ruthenium catalyst.
 15. A polymerelectrolyte fuel cell using the proton conducting polymer membraneaccording to 1 or 2, or the membrane-electrode assembly according toclaim
 13. 16. A direct methanol fuel cell using the proton conductingpolymer membrane according to claim 1 or 2, or the membrane-electrodeassembly according to claim
 13. 17. A method for manufacturing a protonconducting polymer membrane having a product ((S·day)/μmol) of a protonconductivity (S/cm) at 23° C. and a methanol barrier coefficient((cm·day)/μmol) at 25° C. in an aqueous methanol solution of a specifiedconcentration that satisfies at least one of either (A) or (B) below,wherein (A) the product in an aqueous methanol solution of 10% by weightis 2.5×10⁻⁴ (S·day)/μmol or more, or (B) the product in an aqueousmethanol solution of 64% by weight is 4.5×10⁻⁵ (S·day)/μmol or more, themethod comprising bringing a film comprising a hydrocarbon polymer intocontact with a sulfonating agent.
 18. A method for manufacturing aproton conducting polymer membrane having an ion exchange capacity of0.3 milli-equivalent/g or more, and having a crystalline phase, themethod comprising bringing a film comprising a crystalline hydrocarbonpolymer into contact with a sulfonating agent.
 19. The method formanufacturing a proton conducting polymer membrane according to claim17, wherein the hydrocarbon polymer is a crystalline hydrocarbonpolymer.
 20. The method for manufacturing a proton conducting polymermembrane according to claim 17 or 18, wherein the hydrocarbon polymer ispolyphenylene sulfide.
 21. The method for manufacturing a protonconducting polymer membrane according to claim 17 or 18, wherein thesulfonating agent is at least one selected from the group consisting ofchlorosulfonic acid, oleum, sulfur trioxide and concentrated sulfuricacid.
 22. The method for manufacturing a proton conducting polymermembrane according to claim 17, wherein the film is brought into contactwith the sulfonating agent in the presence of a solvent.
 23. The methodfor manufacturing a proton conducting polymer membrane according toclaim 22, wherein the solvent is a halide with three or more carbonatoms.
 24. The method for manufacturing a proton conducting polymermembrane according to claim 22 or 23, wherein the solvent is at leastone selected from the group consisting of 1-chloropropane,1-bromopropane, 1-chlorobutane, 2-chlorobutane,1-chloro-2-methylpropane, 1-bromobutane, 2-bromobutane,1-bromo-2-methylpropane, 1-chloropentane, 1-bromopentane,1-chlorohexane, 1-bromohexane, chlorocyclohexane and bromocyclohexane.25. The method for manufacturing a proton conducting polymer membraneaccording to claim 22, wherein the solvent is 1-chlorobutane.
 26. Themethod for manufacturing a proton conducting polymer membrane accordingto claim 17 or 18, wherein the sulfonating agent is sulfur trioxide, andthe film comprising the hydrocarbon polymer is brought into contact witha gas containing sulfur trioxide.
 27. The method for manufacturing aproton conducting polymer membrane according to claim 17 or 18, whereinthe proton conducting polymer membrane is irradiated with at least oneradiation selected from the group consisting of γ-ray, electron beam andion beam.
 28. The method for manufacturing a proton conducting polymermembrane according to claim 27, wherein the dose of the radiation isfrom 10 kGy to 1,000 kGy.